While anti-aging products have been increasingly demanded due to the recent progress of aging of the society, young people have remarkably increasing interest in the beauty of their skin itself. Thus, the importance of cosmetics, especially those for skin whitening, is increasing.
Internal factors such as aging, and external factors such as ultraviolet and active oxygen cause deterioration of various functions of the skin that have been originally maintained, leading to appearance of various troubles. An example of the skin troubles is pigmentation of the skin, which appears due to spots, freckles, sunburn and the like. It is said that the main cause of pigmentation is production of the melanin precursor by enzymatic reaction of tyrosine present in the skin, followed by production of melanin by oxidation.
Substances that suppress production of melanin can be roughly divided into two types. One of these is the type that directly suppresses the activity itself of tyrosinase enzyme that influences melanin production, and the other is the type that does not directly suppress the tyrosinase activity but suppresses melanin production in pigment cells. There are also substances having both actions. Examples of generally known components that have melanin-production-suppressing action and are effective for prevention or amelioration of pigmentation include ascorbic acid, glutathione and hydroquinone, as well as other various natural plant-derived components proposed so far (e.g., Patent Documents 1 and 2).
On the other hand, earthworm extracts and dry earthworm powders have been used from ancient times in mainly oriental countries as prophylactic agents and therapeutic agents for various diseases, and examples of their uses so far known include uses as bladder-stone-reducing agents and bladder-stone-excretion-promoting agents, therapeutic agents for icterus, oxytocics, tonics, hair-growing agents, aphrodisiacs, antipyretics, therapeutic agents for convulsion, blood circulation promoters, therapeutic agents for hemiplegia, indirect analgesics, diuretics, therapeutic agents for bronchial asthma and therapeutic agents for hypertension.
Patent Document 3 discloses that earthworm extracts obtained by hydrothermal treatment followed by extraction with an organic solvent or by hydrolytic extraction have an action to suppress the tyrosinase activity.